The aims of this proposal are to investigate the mechanisms of gastric survival of Hilicobacter pylori with specific reference to the urease generated at high quantities by this orgasms. Our analysis mechanisms of generation of an electro-chemical gradient of hydrogen ions is to be extended to an analysis of the properties and regulation of the urease with respect to (a) investigation of internal urease of H. pylori as a regulator of bacterial periplasmic pH in an acid milieu; (b) investigation of the mechanisms of internal urease by medium pH including assessment of the role of possible transporters and inner and outer membrane processes; (c) determination of the function of the gene products of the urease operon and especially the membrane inserted gene products in control of urease function; (d) Determination of the mechanism of externalization of the urease of H. pylori and urease effects at neutral pH; (e) analysis of the likely gastric environment of H. pylori as a function of urease activity; (f) assessment of NH3 generation inside H. pylori as a modulator of gastric cellular pH and [Ca]. Various techniques to be applied include fluorimetric measurements of transmembrane potentials and periplasmic pH, urease operon functional analysis by mutagenesis and yeast 2 hybrid analysis, video imaging and confocal microscopy of organisms and cells to which they adhere. Understanding the means of survival and cytotoxicity of this pathogen will enable more rational treatment of peptic ulcer disease.